The present invention is directed to a printing apparatus having means for advancing an elongated recording material. More particularly, the present invention is directed to a recording material advancing means of a printing apparatus having a motor driven tension means which provides the recording material with adequate tension during manual and automatic operation of the advancing means.
As is well known, a printing apparatus, such as a line printer, is widely used as an output device of an information processing system. FIG. 1 is a prior art printing apparatus. With respect to the apparatus in FIG. 1, a printing paper PP (hereinafter, the printing paper referred to is an elongated printing paper) is pulled up from a hopper 5, which is usually located at a lower part of the apparatus, by a recording material advancing means which includes a tractor at an upper part of the apparatus. The printing paper PP passes between a printing head 1 and a platen 2. Since a printing apparatus of this type is provided with a tractor 3 only at the upper part of the printing apparatus, easy input of printing paper PP from the hopper 5 and a simplified structure is realized.
While the printing paper PP is advanced from the hopper 5 by the tractor 3 which is driven by an advancing motor 30, the printing paper PP is apt to flap between the printing head 1 and the hopper 5. This results in lower printing quality. In order to prevent this disadvantage, tension means 4 is provided at a position between the printing head 1 and the hopper 5. The tension means includes, for example, a pair of pinch rollers consisting of a pressing roller 41 and a friction roller 40. The friction roller 40 is braked by frictional force, but is not driven by external power. The pinch roller pinches the printing paper PP between both rollers, acting as a tension load for the advancing printing paper PP. Thus, the printing paper PP passing between the printing head 1 and the platen 2 is subject to a static tension of a predetermined magnitude which suppresses the flapping of the printing paper PP during advancement of the printing paper PP. As a result, any irregular printing is eliminated. Generally, the recording material advancing means (i.e., the tractor 3), can be operated automatically or manually in conjunction with the printing head 1, under the control of a central controller which is not shown in FIG. 1.
Usually, positioning the printing paper PP is carried out before printing, and is manually performed. Thus, the automatic operation of the printing apparatus is suspended while positioning is performed. An operator advances the printing paper PP by rotating a knob 31 connected to a driving shaft of the tractor 3. When the printing paper PP is manually advanced, the printing paper PP may sometimes slacken. If an operator reverses the printing paper PP by manually rotating the knob 31 counter-clockwise, the printing paper PP will slacken as shown at 43 in FIG. 2. In the same manner, even when the printing paper PP is advanced by rotating the knob 31 clockwise, the printing paper PP may also slacken if the rotation of the knob 31 is suddenly suspended. The slack on the paper cannot be eliminated in the printing apparatus of the prior art, resulting in irregular printing, i.e., uneven printing, double printing, etc.
With respect to the manual operation of the tractor 3, another manual operation of the tractor 3 includes driving the tractor 3 by the motor 30 which is controlled by an operator. The operator turns a switch on and off so as to turn the motor 30 on and off, instead of suspending the motor 30 and advancing the tractor 3 by manually rotating the knob 31. However, with respect to slack in the printing paper PP, the cause and the counter measure for the problem are the same in both manual advancing methods. In the following description, therefore, unless otherwise mentioned, the manual operation of the recording material advancing means refers to a manual operation performed by manually rotating the knob 31.
Thus, an improved recording material advancing means for solving the problem of slack in the paper is necessary.